Signal amplification in biological and electrical engineering systems: Universal role of cascades

In this paper we compare the cascade mechanisms of signal amplification in biological and electrical engineering systems, and show that they share the capacity to considerably amplify signals, and respond to signal changes both quickly and completely, which effectively preserves the form of the input signal. For biological systems, these characteristics are crucial for efficient and reliable cellular signaling. We show that this highly-efficient biological mechanism of signal amplification that has naturally evolved is mathematically fully equivalent with some man-developed amplifiers, which indicates parallels between biological evolution and successful technology development.     

Inhibition of repulsive guidance molecule,RGMa, increases afferent synapse formation with auditory hair cells

The peripheral fibers that extend from auditory neurons to hair cells are sensitive to damage, and replacement of the fibers and their afferent synapse with hair cells would be of therapeutic interest. Here, we show that RGMa, a repulsive guidance molecule previously shown to play a role in the development of the chick visual system, is expressed in the developing, newborn, and mature mouse inner ear. The effect of RGMa on synaptogenesis between afferent neurons and hair cells, from which afferent connections had been removed, was assessed. Contact of neural processes with hair cells and elaboration of postsynaptic densities at sites of the ribbon synapse were increased by treatment with a blocking antibody to RGMa, and pruning of auditory fibers to achieve the mature branching pattern of afferent neurons was accelerated. Inhibition by RGMa could thus explain why auditory neurons have a low capacity to regenerate peripheral processes: postnatal spiral ganglion neurons retain the capacity to send out processes that respond to signals for synapse formation, but expression of RGMa postnatally appears to be detrimental to regeneration of afferent hair cell innervation and antagonizes synaptogenesis. Increased synaptogenesis after inhibition of RGMa suggests that manipulation of guidance or inhibitory factors may provide a route to increase formation of new synapses at deafferented hair cells. © 2013 Wiley Periodicals, Inc. Develop Neurobiol 74: 457–466, 2014     

Performance of a time-resolved IR facility for assessment of protonation states and polarity changes in carboxyl groups in a large membrane protein,mammalian cytochrome c oxidase,under turnover conditions in a sub-millisecond time resolution

Time-resolved IR analyses for the protonation and polarity changes of carboxyl groups involved in proton pump enzymes under turnover conditions are indispensable for elucidation of their proton-pump mechanisms. We have developed a new time-resolved infrared facility by introducing a flow system for transferring highly concentrated and thus viscous protein solution to a thin (50?μm) flow cell equipped in a highly sensitive IR spectrometer constructed with the femtosecond mid-IR pulse laser with spectral width of 350?cm^?1 as an IR white light source equipped with multi-channel MCT detector. This facility equipped with O₂ supply system enables the sub-millisecond time scale infrared measurements of the O₂ reduction coupled with proton pumping by bovine cytochrome c oxidase (CcO) initiated by CO-flash photolysis in the COOH (1725–1770?cm^?1) region with the accuracy of about 10?μO.D. under the background O.D. of 1. The facility identifies a band intensity change at ~1744?cm^?1 assignable to protonation of a carboxyl group coupled with a single electron transfer to the O₂ reduction center within 1?ms after initiation of the reaction. The results suggest that the facility detects protonation of a single carboxyl group included in large proteins like as CcO (210?kDa). The present facility sensitively identifies also polarity changes in COOH group by detecting shifts of the bands near 1750?cm^?1 and 1760?cm^?1, without significant intensity changes. These findings show the performance of this facility sufficiently high for providing crucial information for understanding the proton transferring mechanisms of protein carboxyl groups.     

Light-harvesting chlorophyll protein (LHCII) drives electron transfer in semiconductor nanocrystals

Type-II quantum dots (QDs) are capable of light-driven charge separation between their core and the shell structures; however, their light absorption is limited in the longer-wavelength range. Biological light-harvesting complex II (LHCII) efficiently absorbs in the blue and red spectral domains. Therefore, hybrid complexes of these two structures may be promising candidates for photovoltaic applications. Previous measurements had shown that LHCII bound to QD can transfer its excitation energy to the latter, as indicated by the fluorescence emissions of LHCII and QD being quenched and sensitized, respectively. In the presence of methyl viologen (MV), both fluorescence emissions are quenched, indicating an additional electron transfer process from QDs to MV. Transient absorption spectroscopy confirmed this notion and showed that electron transfer from QDs to MV is much faster than fluorescence energy transfer between LHCII and QD. The action spectrum of MV reduction by LHCII-QD complexes reflected the LHCII absorption spectrum, showing that light absorbed by LHCII and transferred to QDs increased the efficiency of MV reduction by QDs. Under continuous illumination, at least 28 turnovers were observed for the MV reduction. Presumably, the holes in QD cores were filled by a reducing agent in the reaction solution or by the dihydrolipoic-acid coating of the QDs. The LHCII-QD construct can be viewed as a simple model of a photosystem with the QD component acting as reaction center.     

提高外淋巴钙浓度对耳蜗电位的影响

本实验以人工外淋巴灌流方式,提高豚鼠耳蜗外淋巴液钙离子浓度（［Ｃａ２＋］ＰＬ）,观察蜗内直流电位（ＥＰ）和耳蜗电图（ＥＣｏｃｈＧ）的变化,ＥＣｏｃｈＧ包括听神经复合动作电位（ＣＡＰ）、耳蜗微音电位（ＣＭ）。结果可见：高钙灌流明显抑制ＣＡＰ幅值,延长同一声强下（９０ｄＢＳＰＬ）Ｎ１－峰潜伏期,但不改变ＣＭ的幅值及总和ＥＰ（Ｇ－ＥＰ）。高钙灌流降低了ＥＰ对噪声的给－撤声反应（ＥＰ－ＯＮ,ＥＰ－ＯＦＦ）和缺氧所得到的最大负ＥＰ（Ｎ－ＥＰ）绝对值。本文分析了外淋巴高钙影响耳蜗电位的可能机制。     

腺苷对豚鼠耳蜗功能的影响

腺苷作为一种神经调质,能抑制多种递质的释放,发挥负反馈调节作用,用外淋巴灌流给药方法,观察了腺苷及其摄取抑制剂双嘧啶氨醇、受体拮抗剂茶 对豚鼠复合听神经动作电位、微音器电位、蜗内直流电位的影响。     

EphA7 regulates spiral ganglion innervation of cochlear hair cells

During the development of periphery auditory circuitry, spiral ganglion neurons (SGNs) form a spatially precise pattern of innervation of cochlear hair cells (HCs), which is an essential structural foundation for central auditory processing. However, molecular mechanisms underlying the developmental formation of this precise innervation pattern remain not well understood. Here, we specifically examined the involvement of Eph family members in cochlear development. By performing RNA‐sequencing for different types of cochlear cell, in situ hybridization, and immunohistochemistry, we found that EphA7 was strongly expressed in a large subset of SGNs. In EphA7 deletion mice, there was a reduction in the number of inner radial bundles originating from SGNs and projecting to HCs as well as in the number of ribbon synapses on inner hair cells (IHCs), as compared with wild‐type or heterozygous mutant mice, attributable to fewer type I afferent fibers. The overall activity of the auditory nerve in EphA7 deletion mice was also reduced, although there was no significant change in the hearing intensity threshold. In vitro analysis further suggested that the reduced innervation of HCs by SGNs could be attributed to a role of EphA7 in regulating outgrowth of SGN neurites as knocking down EphA7 in SGNs resulted in diminished SGN fibers. In addition, suppressing the activity of ERK1/2, a potential downstream target of EphA7 signaling, either with specific inhibitors in cultured explants or by knocking out Prkg1, also resulted in reduced SGN fibers. Together, our results suggest that EphA7 plays an important role in the developmental formation of cochlear innervation pattern through controlling SGN fiber ontogeny. Such regulation may contribute to the salience level of auditory signals presented to the central auditory system. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 452–469, 2016     

Selecting a Hiding Place: Anuran Diversity and the use of Bromeliads in a Threatened Coastal Sand Dune Habitat in Brazil

Among vertebrates, anuran amphibians represent the highest number of species associated with bromeliads and possess a range of ecological, behavioral, and morphological specializations to life in these plants. Despite the importance of bromeliads as biodiversity amplifiers, and their diversity in some habitats, studies of the relationship between anurans and these plants are scarce in Brazil. Here, we investigated the way anurans select and use bromeliads in a threatened coastal habitat. We analyzed data from 23 standardized samples of the anurans associated with the bromeliad Neoregelia cruenta in the Restinga de Maricá, State of Rio de Janeiro, Southeastern Brazil. We found nine anuran species using these bromeliads, representing the highest richness reported for a Brazilian restinga. We identified a general pattern of bromeliad usage, where plants located at the edges of scrub patches (exposed to the sun) were more frequently occupied by anurans than those located more to the center (in the shade). There is strong evidence of an active selective process based on the quality of the water stored in the rosette, which differs between plants depending on their position in the scrub patch. Although the number of individuals varied during the period of study, the frequency of bromeliads used was constant, indicating that plant occupation follows a regular pattern throughout the year. Furthermore, the high frequency of bromeliads used by anurans during the whole year highlights the importance of considering these plants in developing conservation programs concerning the protection of anurans.